/**
 * 服务注册中心
 * 支持服务的注册和发现功能
 */
import java.util.*;
import java.util.concurrent.ConcurrentHashMap;

public class ServiceRegistry {
    // 使用ConcurrentHashMap存储服务信息，确保线程安全
    private final Map<String, List<ServiceInstance>> services;
    
    // 单例模式实现
    private static volatile ServiceRegistry instance;
    
    private ServiceRegistry() {
        services = new ConcurrentHashMap<>();
        System.out.println("服务注册中心初始化完成");
    }
    
    // 获取单例实例
    public static ServiceRegistry getInstance() {
        if (instance == null) {
            synchronized (ServiceRegistry.class) {
                if (instance == null) {
                    instance = new ServiceRegistry();
                }
            }
        }
        return instance;
    }
    
    // 注册服务
    public synchronized void register(String serviceName, String host, int port) {
        ServiceInstance instance = new ServiceInstance(host, port);
        services.computeIfAbsent(serviceName, k -> new ArrayList<>()).add(instance);
        System.out.println("服务注册成功: " + serviceName + " at " + host + ":" + port);
    }
    
    // 注销服务
    public synchronized void deregister(String serviceName, String host, int port) {
        List<ServiceInstance> instances = services.get(serviceName);
        if (instances != null) {
            boolean removed = instances.removeIf(instance -> 
                instance.getHost().equals(host) && instance.getPort() == port);
            if (removed) {
                System.out.println("服务注销成功: " + serviceName + " at " + host + ":" + port);
                // 如果该服务没有实例了，移除服务
                if (instances.isEmpty()) {
                    services.remove(serviceName);
                }
            } else {
                System.out.println("服务不存在: " + serviceName + " at " + host + ":" + port);
            }
        } else {
            System.out.println("服务不存在: " + serviceName);
        }
    }
    
    // 发现服务（获取所有实例）
    public List<ServiceInstance> discover(String serviceName) {
        List<ServiceInstance> instances = services.get(serviceName);
        if (instances != null && !instances.isEmpty()) {
            System.out.println("发现服务: " + serviceName + "，实例数量: " + instances.size());
            return new ArrayList<>(instances); // 返回副本避免并发修改问题
        }
        System.out.println("未发现服务: " + serviceName);
        return Collections.emptyList();
    }
    
    // 获取随机实例（简单的负载均衡）
    public ServiceInstance getRandomInstance(String serviceName) {
        List<ServiceInstance> instances = discover(serviceName);
        if (!instances.isEmpty()) {
            Random random = new Random();
            ServiceInstance instance = instances.get(random.nextInt(instances.size()));
            System.out.println("选择随机实例: " + serviceName + " at " + instance.getHost() + ":" + instance.getPort());
            return instance;
        }
        return null;
    }
    
    // 获取所有已注册的服务名称
    public Set<String> getAllServices() {
        return new HashSet<>(services.keySet());
    }
    
    // 服务实例内部类
    public static class ServiceInstance {
        private final String host;
        private final int port;
        private final long registerTime;
        
        public ServiceInstance(String host, int port) {
            this.host = host;
            this.port = port;
            this.registerTime = System.currentTimeMillis();
        }
        
        public String getHost() {
            return host;
        }
        
        public int getPort() {
            return port;
        }
        
        public long getRegisterTime() {
            return registerTime;
        }
        
        @Override
        public String toString() {
            return host + ":" + port;
        }
        
        @Override
        public boolean equals(Object o) {
            if (this == o) return true;
            if (o == null || getClass() != o.getClass()) return false;
            ServiceInstance that = (ServiceInstance) o;
            return port == that.port && Objects.equals(host, that.host);
        }
        
        @Override
        public int hashCode() {
            return Objects.hash(host, port);
        }
    }
}